Electric resistance.



No. 787,047. PATENTED APR. 11, 1905.

' H. W. LEONARD.

ELECTRIC RESISTANCE.

APPLIOATION FILED 11110.8,1904.

(av/L Wi ma eooeo Patented April 11, 1905.

PATENT OFFICE.

HARRY WARD LEONARD, OF BRONXVILLE, NEI'V YORK.

ELECTRIC RESISTANCE.

SPECIFICATION forming part of Letters Patent No. 787,047, dated April11, 1905.

Application filed December 8, 1904. Serial No. 235,930-

I'o (bi/Z whom, it 71711.7 concern:

Be it known that I, HARRY WVAED LEONARD, a citizen of the United States,residing at Bronxville, in the county of estchester and State of NewYork, have invented certain new and useful Improvements in ElectricResistances, of which the following is a full, clear,

and exact specification.

My invention relates to improvements in resistances, especially such asare heated by electric currents in apparatus such as rheostats,electricheaters,&c. My invention, however, has many other uses, as willbe apparent from the description later herein.

There are now in use many forms of resistanc'es in which the resistanceis embedded either wholly or partially in some insulating material whichclosely surrounds the resistive conductor. Examples of such resistancesare shown and described in the following United States patents: No. 447,023, to Carpenter; No. 477,247. to Cummings, and Nos. 691,949 and707,244, to myself. In all such cases it is difficult to use a singleresistive conductor of large cross-section such as would be suitable forcarrying a large current -sucli as fifty amperes, for example becausethe mechanical strains developed in the insulating material contiguousto this resistive conductor would be so great as to have a tendency tocrack or otherwise impair the perfection of the mechanical contact orthe electrical insulation, or both.

I have found that certain resistive alloys which are very satisfactoryif used so as to be free to expand and contract, as is usually the case,will be very troublesome when, for example, they are to be enameled uponthe surface of a porcelain tube or other similar surface, especiallywhen the wire is Wound around the outside surface and when the materialof the support has a low coefficient of expansion. For example, I havefound by suitable tests that there is such a great difference in theexpanson of various metallic alloys which I customarily use in makingrheostats that I frequently have difficulty in making satisfactorily anenam eled resistance-tube such as I have described in my Patent No.691,949, because the specific expansion of the material of the resistiveconductor is so high relative to that of the material of the desiredsupport that the wire becomes very loose and distorted when subjected tothe heat of manufacture in a muffle-furnace. Also after thisresistancetube is made there is a strong tendency for the enamel tocrack ofl above the wire and for the wire to become loose on the tubewhen the wire is a large one and the material of the conductor has ahigh specific expansion. Of course when the wire becomes exposed andloose it is not so good commercially as it would be if the coatingofenamel should remain practically unaffected by the expansion of theheated conductor. These difficulties have overcome by my presentinvention, and some of the advantageous results thereof will beunderstood from the following description.

Referring to the accompanying drawings, which show the preferred form ofmy invention, Figure 1 is a side view of a resistance unit embodying myinvention, no insulatingcoating being shown, however. Fig. 2 is alongitudinal section of the completed article. Fig. 3 is a detailshowing the form ofterminal connection. Fig. 4 is an enlarged view of aportion of Fig. 2. Fig. 5 is an enlarged view of the resistiveconductor. and Fig. 6 is a plan view of a modified form of constructionwith the insulating coating removed.

A tube of porcelain or other suitable material is indicated at 1. Uponthis is located the resistive conductor 2, wound spirally. Thisconductor is composed of refiexed strands and preferably in the form ofa flat braid having a loose open mesh. I prefer to make the conductor ofalloy and composed largely of copper and nickel or some other form ofresistance having a temperature coefficient as low as practical. Theconductor is embedded in the insulating, heat-resisting, and protectivecoating 3 of material having thedesired prop erties and which serves toconduct heat from the conductor and dissipate this heat. Theseproperties are to be found in various solid mineralinsulating materials,and I therefore prefer to use such materials. Glass enamel is preferableand serves to hermetically seal the conductor and adhesively engages thesupport. This coating 3 does not merely cover the braided or strandedconductor, but is worked all through the loose mesh thereof andpractically ineloses each individual strand. Any one of a large numberof different insulating-coatings may be used. Also after it has beenmanufactured it can be subjected to alternate heatings and coolings bypassing a current through the conductor and the perfection of thecoating is not affected in any way. I can use conductors of even thehighest specific expansion embedded in coatings of a very brittle natureupon supports having an extremely different specific expansion from thatof the resistive conductor. I have used conductors having the highestspecific expansion and supports having the lowest specific expansion,and vice versa, and in every case I have obtained a perfectlysatisfactory result. The reason for this is no doubt that the mechanicalstrain of each individual strand is so slight and the several strandsare so distributed through the coating that the strain developed byheating the conductor is not sufficient to be troublesome.

Another important result obtained by my invention is that whereasheretofore I was obliged to use for large currents material ofrelatively high temperature coeflicient I can by practicing my inventionuse resistive conductors of practically no temperature coefficient evenwhen the currents are very large.

In explanation I can say that the commercial resistive conductors whichhave the lowest temperature coeilicient have invariably, so far as Iknow, a high specific resistance or resistivity. One of the best alloysas regards low temperature coefficient, high fusion temperature, nonoxidizing qualities, tensile strength, ductility, hardness, and otherdesirable qualities for use in enamel-coated resistances, such as Ioften desire to employ it for, is an alloy composed essentially ofnickel and copper in substantially the proportions of sixty copper andforty nickel; but this alloy has relatively a much higher specificexpansion than others I might employ if I could disregard the importanceof the above cited qualities. It also has a high resistivity, itsresistivity at ordinary temperatures being about thirty times that ofcopper. It will be apparent that a single wire of this material capableof carrying, say, fifty, amperes is necessarily very large incross-section relative to copper, for example.

The smaller copper wire might be successfully enameled upon aninsulating-support; but it would be objected to because of its hightemperature coeflicient.

The copper-nickel-alloy wire would be so large in order to carry fiftyamperes satisfactorily as regards possible fusion by the current thatits expansion when heated in practice would cause a destructive strain.One way of overcoming some of these difiiculties is to usea reflexedmetallic ribbon, at

tached edgewisc by the enamel to the surface of the tube, patented to mein United States Patent No. 7072M; butthis form is not always desirable,because the conductor is exposed to the air, and it is extremelydelicate and liable to be injured if the resistance has to be packed,shipped, or handled, especially if it has to be handled by inexperiencedparties as is often the case. By my new resistance-conductor in the formof a wide loose flat braid I overcome all of these difliculties andobtain all of the most desirable qualities-such as high insulation, lowtemperature coefficient, freedom from depreciation of the conductor byoxidation or other chemical action, freedom from depreciation of theinsulating coating due to the heating strains, compactness, and lowcost.

Another very important advantage is that due togreatly-reduced firerisk, which is explained as follows: Of course every suchrcsistance-tube can be burned out if suflicientl y large currents bepassed through it, and in practice it must be expected that improperusage or failure of other allied devices may result in burning out theresistance. hen such aburn out does occur, it is of the greatestimportance in many instances that the arc shall be reduced to theminimum, that it shall be extinguished as promptly as possible, and thatit shall be kept below the surface of the insulating-coating as much aspossible. ln many instances, such as in uses on board of naval ships,this quality of burning out witlr out risk of igniting explosive orinflammable material in the vicinity is of the first importance. It isessential for such cases that the conductor be of the inclosed type-that is, surrounded by solid insulating 1'naterial-'and glass enamel isthe most desirable material thus far employed; but a large single wirefused by excessive current on an enameled tube makes an are which issometimes quite disruptive in character and throws off molten pelletsthat are a serious risk. By means of my invention I greatly reduce thisrisk. \Vhen the stranded conductor isfused by excessive current, a largenumber of different divided arcs of much correspondingly sn'lallerenergy result, and the well-known extinguishing effect due to dividingan are into a number of smaller ones and subjecting each to the coolingeffect of having it surrounded by its own inclosing mass of material isvery beneficial and results in a practical freedom from all fire risk.Each small strand acts, in fact, like a small inclosed type-fuse.

The flat form of braid of course enables me to perfectly cover aconductor of high ampere capacity with a thin layer of enamel, and thisagain results in a much tougher coat of enamel than could be obtainedwith a thicker coat. All that I have said as to the advantages I obtainwhen using glass enamel apply equally well to other forms ofinsulating-coating, and

it will be apparent that there are many advantages in using my inventionfor uses not described by me or uses in which only a few of thequalities I have named as desirable may be of especial importance.

SometimesI use my stranded resistive conductor in sheet-glass or othersimilar solid glass insulation. Sometimes I mold the insulating materialabout the conductor and then subject the insulating material to theusual processes of its manufacture.

In some cases my new form of resistive conductor will have advantageseven when it is not embedded in or attached by adhesive insulatingmaterial.

Although the cost of the same weight of wire will be greater whenstranded than when in a single wire, there are several reasons why I amable to reduce the cost of manufacture by using the stranded conductor.The first reason is that the surface of the conductor from which theheat is enameled is greatly increased relative to that of a single wireof the same cross-section and weight per foot. Therefore to dissipatethe same energy from the surface of the conductor I can use a muchsmaller weight per foot. This increases the ohms per foot, and henceenables me to reduce the number of feet to obtain the desiredresistance. This reduction of total cross-section and reduction oflength results in such a great saving in weight that the strandedconductor is materially cheaper for a certain duty than a single wirewould be.

7 Another reduction of cost of manufacture is that due to the muchgreater ease in securing a perfect coating of enamel. WVith large wiresthick coats of enamel are needed. These are much more expensive both asregards ma terial and labor, and they require longer time in the furnaceand usually require more coats and firings than the flat braidedconductor requires. Also there is a smaller percentage of defectivepieces which are wasted in manufacture and few defects develop in usage.

Another important feature of my invention is the form of the terminallead-wires. Heretofore it has been universally customary to use a singlesolid lead for such rheostats, electric heaters, &c., the material beingcopper. I now use a braided copper terminal lead, preferablyaroundbraid. This is shown at l on the drawings and part encircles the tubeand lodges in the groove 5, formed at the end thereof. By providing thisgroove or other depression in the support for the location of theterminal lead I secure very desirable results. It prevents the shiftingof the terminal. The lead and joint, with the resistive conductor, maybe easily and thoroughly covered with the insulating-coating. It permitsthe use of a very thin coating along the rest of the tube, while havinga thick coating within which the joint and terminal lead may lie. Itreduces the diametrical dimension at the ends of the unit, where itwould otherwise be greatest, and secures additional protection of thelead and joint. It aids in manufacture by giving a definite distancebetween the end of the tube and the terminal and between the twoterminals and insures that the terminal lead and joint will be perfectlyattached and protected by the coating. The principal objects of usingstranded, reflexed, copper terminal wire are to secure the greatestpossible flexibility, to reduce to a minimum the strain which may bebrought upon the wire under the enamel and in the enamel itself when theterminal lead-wire is bent back and forth, as it frequently must be inconnecting up the resistance, disconnecting it and handling itotherwise, also to reduce to a minimum the liability of the terminallead-wire breaking off, due to bending or vibration or other strain.This desirability of the braided or otherwise stranded copper terminallead-wire is especially pronounced in apparatus in which the copper wirehas during the course of manufacture been subjected to such a heat asthat of a muffle-furnace and then allowed to cool in the air. A copperwire which will stand repeated bending without breaking off when it isin the condition as received from the maker of the copper wire,especially when it has been properly soft-annealed or otherwise treatedto make it as ductile as possible, will alter greatly as to this qualityof withstanding bending if it be subject to a mufl-le-furnace heat, asindicated. After such heating the wire is very apt to break off if it bebent back and forth in a way which would have no appreciable effect uponit before it was so heated. The solid terminal lead formerly in usewould oftentimes break off when the purchaser or user was bending theterminal lead. Usually this break would be just where the copper wireentered the enamel. This would render the resistance worthless. Evenwhen the wire did not break off at the place where it entered the enamelit would often subject the enamel at that point to such a strain as torupture the enamel, and thus cause a depreciation of the resistance,which often led to a burning out of the resistance-wire at that point.Sometimes the strain due to the too rigid terminal lead-wire wouldrupture the very fine resistance-wire even before the current wasapplied. There was formerly also this difliculty. The simplest andcheapest way of connecting the lead was to wind it around the tube andfasten to it, by means of a hammered joint, to the smallerresistance-wire. When the resistance unit was one for, say, fiftyamperes, the copper terminal lead wires were necessarily rather largeand difiiculty was met with on account of the rigidity of the wire inmaking it lie close to the tube at all places. At the place where thejoint was made there was a tendency for the wire to stand away from thesurface, and this made it diflicult to get this part well enameled. Alsothe solid wire when heated in the mufiie-furnace expanded so strongly asto crack the coating of the dried enamel powder, which had previouslybeen applied in the form of a viscous paste. Such a small crack as thiswould tend to follow any wire of considerable size, and when finally thehigher heat fused the enamel powder into a glass coating the coatingwould pull apart at the edges of such cracks. This would necessitateadditional coatings and firings, entailing additional expense andresulting in an inferior article. There was also difficulty in making agood hammered joint between the large single copper wire and theresistance-wire of different size and material. All of thesedifficulties I overcome by using the stranded copper terminal lead-wire.It is very superior as regards resisting repeated bends withoutbreaking. It reduces to a minimum any strain upon the terminal lead orthe enamel where the terminal lead enters the enamel. W'hen wound aroundthe tube, it hugs the surface perfectly. When heated, it does notproduce suflieient strain by its expansion to crack the dried enamelpowder coating, as there is a flexibility endwise along the axis of theconductor due to its braided form, as there always is in a reflexed wirerelative to a straight one. The braided wire is practically reflexed inevery plane instead of one plane only. The several strands laid over theresistance-wire enable me to secure a very perfect hammered joint.

Fig. 3 shows my preferred form of terminal connection. The lead I haswrapped around it at 5 a short piece of similar braided round copperwire 6. The connection is made between the resistive conductor and lead4 by the clip 7, which is hammered over the union of the lead andconductor. The parts are tightened about the tube by twisting togetherthe ends of the lead t and the piece 6, as shown at 8. It will be notedthat the piece 6 is wrapped around the lead t at 5, so that one end ofpiece 6 is toward the joint 7. Consequent] y when the parts aretightened up by twisting theends together at 8 the union at 5 willclosely engage the surface of the tube. Also on account of theflexibility of the terminal connection the parts encircling the tubewill closely engage its surface. The only joint in the parts whichconduct the current is that at 7 the lead 4: making direct connectionwith the conductor 2 at the joint 7. This joint is some distance awayfrom the union at 5 and is entirely free from injurious strains due tomovement of the outside portion of lead t.

Sometimes Iuse a plurality of conductors in multiple between theterminal, each being preferably wound as a thread on a cylindricalsurface and there being two, three, or more such threads parallel toeach other.

Sometimes I make a tubular braid and then put inside of it a cylinder asa support, and I then sometimes attach this braid to the surface of thecylindrical support by an insulating-coating.

In some cases I use a tubular braid with an open mesh as the resistiveconductor of a rheostat without any support inside of it. The tubularshape makes it self-siniporting, and there is a very large surface wellexposed to the air.

Sometimes I make such a tubular braid or a flat braid or other form ofstranded resistive conductor and place it in a heat-absorptiveinsulating material, such as sand or oil or any suitable material whichmakes good contact with the heat-emitting surface of the resistiveconductor.

Sometimes I mount the resistive conductor upon a support having a flatsurface, and I may divide the conductor into a number of parts. Fig. 6shows a form of construction in which the flat braided conductor 2 ismounted upon a support 9, having a flat surface instead of the form of acylimler. The several conductors 2 are united to the leadwires 10 by theclips 7 in the form of a hammered joint. The leads 10 are of copper andin the form of a round-braided wire. The insulating-coating, such asglass enamel. is not indicated in this figure; but it will be understoodthat the resistive conductors, joints, and portions of the terminalleads are embedded in such a coating, as previously explained. This formof construction is very desirable where it is desired to vary theresistance of the unit or to adjust its resistance to an amount desiredto meet certain conditions. Six resistive conductors are shown, and bymeans of the loads 10 they all maybe connected in multiple, giving thelowest resistance and maximum current capacity. They may be connectedthree in multiple and the two sets of three in series, giving anincreased resistance and decreased currentcapacity. They may beconnected two in multiple and the three sets of two in series, giving afurther increase in resistance and a further decrease in currentcapacity, and finally they may all be connected in series, givingmaximum resistance and lowest current capacity. The

leads 10 are made extra long to permit the I various connectionsdesired.

As my invention is susceptible of many modifications, I do not intend orwish my invention to be limited except as expressed by the followingclaims.

Having thus described my invention, .1 declare that what I claim as new,and desire to secure by Letters Patent, is-

1. In a device in which electric energy is intentionally converted intoheat, a stranded resistive conductor, the individual strands of saidconductor composed of amaterial having a relatively low temperaturecoefiicient.

2. In a device in which electric energy is intentionall y converted intoheat, a stranded resistive conductor, the individual strands of saidconductor composed of a material having a relatively low temperaturecoeliieient and a relatively high specific resistance.

3. In a device in which electric energy is intentionally converted intoheat, astranded resistive conductor, the individual strands of saidconductor composed of a material having a relatively low temperaturecoeiiicient and a relatively high specific resistance and coeflicient ofexpansion.

4:. The combination of a stranded conductor having interstices betweenthe strands, means for supporting said conductor, and a heat-resistinginsulating material within said inter- Stices.

5. The combination of a stranded conductor of high specific resistanceand low temperature coeiiicient, means for supporting said conductor,and an insulating heat-resisting material embedding and surrounding saidconductor.

6. The combination of astranded conductor of high specific resistanceand low tern perature coeflicient, a support for said conductor, and aninsulating heat-resisting material embedding and surrounding saidconductor and fixing the same in position upon said support.

7. The combination of astranded conductor of high specific resistanceand low temperature coeflicient, a support for said conductor composedof insulating material, and an insulating heat-resisting materialembedding and surrounding said conductor and seeu ring the same inposition upon said support.

8. The combination of a conductor in the form of a flat braid, means forsupporting said conductor, and a mineral insulating material embeddingand surrounding said conductor.

. 9. The combination of a conductor in the form of a fiat braidhavinginterstices between the strands, means for supporting saidconductor, and a heat-resistinginsulating material filled within saidinterstices and surrounding said conductor, said material serving toconduct and dissipate heat from said conductor.

10. The combination of astranded resistive conductor, said conductorcomposed of an al loy, means for supporting said conductor, and a copperterminal lead-Wire electrically con nected to said conductor.

11. The combination of a stranded resistive conductor, said conductorcomposed of an alloy, means for supporting said conductor, and acopper-stranded terminal lead-wire electrically connected to saidconductor.

12. The combination of a braided resistive conductor, said conductorcomposed of an alloy, means for supporting said conductor, and acopper-braided terminal lead electrically connected to said conductor.

13. In a rheostat or electric heater, the combination with the resistiveconductor, of a stranded copper lead electrically connected to saidconductor.

14. In a rheostat or electric heater, the combination with theresistiveconductor, of a copper lead composed of strands braidedtogether and electrically connected to said conductor.

15. in a rheostat or electric heater, the combination with the resistiveconductor, of a copper lead electrically connected with said conductor,said lead composed of a plurality of copper conductors.

16. In a rheostat or electric heater, the combination with the resistiveconductor, of a lead electrically connected to said conductor, said leadcomposed of reflexed copper wires.

17. The combination of a resistive conductor, means for supportingsaidconductor, solid insulating material surrounding said conductor, and astranded copper terminal lead electrically connected to said conductor.

18. The combination of a stranded conductor of high specific resistanceand low temperature coeflicient, means for supporting said conductor, aninsulating heat-resisting material embedding and surrounding saidconductor, and a stranded copper terminal lead-Wire electricallyconnected to said conductor.

19. The combination of a stranded conductor, said conductor composed ofan alloy containing nickel, means for supporting said conductor, aninsulating heat-resisting material embedding and surrounding saidconductor, and a stranded terminal lead-wire electrically connected tosaid conductor.

20. The combination of a stranded conductor, said conductor composed ofan alloy containing nickel and copper, means for supporting saidconductor, an insulating heat-resisting material embedding andsurrounding said conductor, and a stranded copper terminal lead-Wireelectrically connected to said conductor.

21. The combination of a conductor in the form of a flat braid, meansfor supporting said conductor, a mineral insulating material eml'ieddingand surrounding said conductor, and a braided copper terminal leadelectrically connected to said conductor.

22. The combination of a conductor in the form of a flat braid, meansfor supporting said conductor, a mineral insulating material embeddingand surrounding said conductor, and a braided copper tern'iinal leadelectrically connected to said conductor, said connection being formedby a hammered joint.

23. The combination of a resistive conductor having a relatively highspecific expansion, said conductor being subdivided and relieved, asupport having a relatively low specilic expansion, and an adhesivecoating embedding said conductor and adhesively engaging said support.

24. The combination o1 a resistive conductor composed of a plurality ofreflexed wires, the material of said conductor being an alloy having arelatively high coeflicient of expansion, :1 high specific resistanceand low temperature coefiicient, a support of relatively low spelead tosaid support comprising a wire, one cilic expansion, and an adhesivecoating embedding said conductor and adhesively engaging said support.

25. The combination of a resistive conductor composed of a plurality ofreiiexed wires, the material of said conductor being an alloy having arelatively high coefficient of expansion, a high specific resistance andlow temperature coefficient, a support of relatively low specilicexpansion, and an adhesive coating embedding said conductor andhermetically sealing the same, and adhesively engaging said support.

26. As a new article of manufacture, a stranded conductor havinginterstices between the strands, said conductor composed of an alloy. 1

27. As a new article of manufacture, a stranded conductor, saidconductor composed of a metallic alloy having a high specificresistance.

28. As a new article of manufacture, a stranded conductor, saidconductor composed of a metallic alloy having a high specific resistanceand a low temperature coefiicient.

29. As a new article of manufacture, a resistive conductor composed ofan alloy and in the form of a flat braid.

30. As a new article of manufacture, a resistive conductor composed ofan alloy and in the form of a flat braid, said alloy having designedlyrelatively low temperature coefiicient.

31. As a new article of manufacture, a resistive conductor composed ofan alloy and in the form of a flat braid, said alloy containing nickeland having designedly a low temperature coefficicnt.

32. As a new article of manufacture, a resistive conductor composed ofan alloy and in the form of a flat braid, said alloy containing nickeland copper and having designedly a low temperature coeflicient.

33. As a new article of manufacture, a resistive conductor composed ofan alloy and in the form of a flat braid, said alloy containing nickeland copper as the principal ingredients, and having designedly a lowtemperature coefficient.

34:. The combination of a resistive conductor, a support for saidconductor, a terminal lead electrically connected to said conductor,said connection being some distance from one end of said lead, and meansfor securing said lead to said support comprising a wire, one end ofsaid wire being twisted to one end of said lead, and the other end ofsaid wire being twisted upon said lead above said connection.

35. The combination of a resistive conductor, a support for saidconductor, a terminal lead electrically connected to said conductor,said connection being some distance from one end of said lead, and meansfor securing said end of said wire being twisted to one end of said leadand the other end of said wire being twisted upon said lead above saidconnection and in such a direction along said lead as to closely engagesaid support.

36. The method of preventing detrimental strains in the insulatingmaterial in which a conductor is embedded, which consists in dividingthe conductor into a plurality of strands, embedding said strands in aninsulating medi um, and dividing the current in multiple between theseveral strands.

37. The method of preventing detrimental strains in an insulating mediumin which a conductor is embedded, which consists in embedding theconductor in an insulating medium, dividing the current between aplurality of strands composing the resistive conductor, and subdividingand distributing the total strain.

38. The combination of a stranded conductor having interstices betweenthe strands, and a heat-resisting insulating material within saidinterstices.

39. The combination of a stranded conductor of high specific resistanceand low temperature coeflieient, and an insulating heatresistingmaterial embedding and surrounding said conductor.

40. The combination of a conductor in the form of a flat braid, and amineral insulating material embedding and surrounding said conductor.

41. The combination of a resistive conductor, solid insulating materialsurrounding said conductor, and a stranded copper terminal leadelectrically connected to said conductor.

42. The combination of a stranded conductor of high specific resistanceand low temperature eoeflicient, an insulating heat-resisting materialembedding and surrounding said conductor, and a stranded copper terminallead-wire electrically connected to said conductor.

43. The combination of a stranded conductor, said conductor composed ofan alloy containing nickel, an insulating heat-resisting materialembedding and surrounding said conductor, and a stranded terminallead-wire electrically connected to said conductor.

4A. The combination of a stranded conductor, said conductor composed ofan alloy containing nickel and copper, an insulating heatresistingmaterial embedding and surrounding said conductor, and a stranded copperter minal lead-wire electrically connected to said conductor.

45. The combination of a conductor in the form of a flat braid, amineral insulating material embedding and surrounding said conductor,and a braided copper terminal lead electrically connected to saidconductor.

46. The combination of stranded resistive conductors, an insulatingheat-resisting ma terial embedding said conductors, and meanselectrically connected to said conductors for connecting them in seriesor in parallel.

4L7. The combination of stranded resistive conductors, an insulatingheat-resisting material embedding said conductors, and stranded terminalleads electrically connected to said conductors.

48. The combination of a support having a flat surface, strandedresistive conductors, an insulating heat-resisting material embeddingsaid conductors, and stranded terminal leads electrically connected tosaid conductors.

49. The combination of a support having a flat surface, resistiveconductors in the form of a flat braid, said conductors composed of analloy having a low temperature coefficient, and stranded copper terminalleads electrically connected to said conductors.

50. In a rheostat or electric heater, the combination of a resistiveconductor composed of an alloy containing nickel and copper and having arelatively high coefiicient of expansion, a relatively high specificresistance and a relatively low temperature coefficient, a support ofinsulating heat-resisting material for said conductor having arelatively low coefficient of expansion, an exposed terminal forming anelectrical joint with said resistive conductor, a coating of insulatingheat-resisting material covering and surrounding said resistiveconductor and said joint, the said conductor being refiexed, wherebydestructive strains in the coating is prevented When the resistiveconductor is heated by the current.

seated in said depression.

52. The combination of a resistive conductor, a support for saidconductor, said support having a depression, and a terminal lead formingan electrical joint With said conductor, the joint and part of said leadbeing seated in said depression.

53. The combination of a resistive conductor, a support having adepression, a terminal lead forming an electrical joint with saidconductor, the joint and part of said lead seated in said depression,and a coating of insulating material covering said resistive conductorand said joint.

5%. In a rheostat 01' electric heater, the combination With theresistive conductor, of a stranded lead electrically connected to saidconductor.

55. In a rheostat or electric heater, the combination With the resistiveconductor, of a lead composed of strands braided together andelectrically connected to said conductor.

56. In a rheostat or electric heater, the combination with the resistiveconductor, of a lead electrically connected to said conductor, said leadcomposed of a plurality of reflexed Wires.

57. The combination of a resistive conductor, means for supporting saidconductor, solid insulating material surrounding said conductor, and astranded terminal lead electrically connected to said conductor.

58. The combination of a stranded conductor of high specific resistanceand low tem- H. WVARD LEONARD.

\Vitnesses:

L. K. SAGER, JULIAN S. W oos'rna.

